mating pipe of slightly different wall thicknesses and its effect on In Line Inspection tools 3

[SNORGY]

Hi folks. Quick one here...

Have a 16" Sch 30 riser (9.53 mm W.T.), and it is proposed to use SCH 40 (12.7 mm W.T.) for a 5 meter straight length of pipe between riser and pig barrel.

P/L riser designer states that ILI will be impossible, irrespective of how the transition weld is beveled or otherwise made.

Will ILI still be achievable with a properly made transition?

 

[BigInch]

3mm difference in wall thickness is impossible for an ILI to negotiate? What kind of idiocy is going on there?

"Quest Integrity Group was contracted to inspect approximately 3.5 miles of 12-inch pipe running from a tank farm to a refinery. The pipeline is constructed of ERW and seamless pipe with nominal wall thicknesses varying from [highlight #FCE94F]0.219-inch to 0.500 inch.[/highlight] The pipeline supplies the crude feed from the offsite tank farm to the refinery."

I'd also say without question that considerably more variation is possible.

http://www.questintegrity.com/artic...llow-Assessing-Unpiggable-Pipelines&preview=1

 

[brimmer]

If that was the case, most of the ILI runs I manage would fail.... when are you going to have all the same wall thickness around risers / barrels?? The sched 40 isn't ideal, but fine, just as long as the ILI vendor knows about it beforehand. As an example, I just ran a tool on a 16" line with changes in WT from 7.1mm to 12.7mm with no transitions.

 

[LittleInch]

i don't understand why the riser designer is saying that - makes no sense to me. The key issue is the transition. The sch 40 needs to be internally machined down to sched 30 thickness in a ratio of 1:4 or better. ILI vendors are wary of step changes as they can damage the feels or seals, but that sort f thickness change is almost within thickness margins.

Please ask the designer why and let us know - just for curiosity

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SNORGY]

Thanks guys. I thought I was losing my mind for a minute, since *THEY* were the ones who were telling *ME* that *I* was the dummy.

In any event, what you have said aligns completely with API SP-0102 2010, Paragraph 7.6.2.1 (for example). I was just trying to envision miles and miles of 16" pipeline in which every girth weld is 100% smooth and aligned on the inside, no over-penetration, no undercut, no +/- 3.2 mm bumps, because we all know how perfect field construction always is, right?

In short, the riser designer selected pipe on the basis of "Class Location 2" in a "General" area, whereas if I had been writing a specification, in the absence of doing the Class Location Assessment, I would have opted for Class Location 3 in a Station - which I think is more appropriate for a riser inside the fence of a 200 MMSCFD gas plant. But that's just me. Anyway, as a direct consequence of this design, and the fact that mill tolerances and corrosion allowances were not considered in establishing the wall thickness, it drives higher strength pipe with proven notch toughness properties into the design of OUR piping if we are to match THEIR piping, and this cascades into valve selection for multiple ESDVs and let-down valves that must be able to pass the ILI. Hence, the question.

So, we said we would match the design - but I don't like the basis or the consequences of it, and I don't like my designs "forced" by others as was the case here, unless there is a good reason, which as nearly as I can tell, there isn't.

 

[SNORGY]

7.2.6.1 actually. Stupid glasses.